1. Field of the Invention
The present invention relates to a method and apparatus for controlling current in a switched reluctance motor (SRM), and more particularly to a method and apparatus for controlling current in a switched reluctance motor (SRM) capable of reducing a noise caused by torque ripple when accelerating/decelerating the motor by sensing the position and speed of the motor through an optical sensor when driving the SRM and then supplying different current waveforms to each motor coil according to the sensed speed of the motor, thereby enhancing efficiency of the motor when rotating the motor at high speed.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating the structure of a conventional switched reluctance motor (SRM). As shown in the drawing, the SRM includes a microcomputer 10 for transmitting a current control signal according to the position and speed sensed by an optical sensor (not illustrated); and an inverter circuit unit 20 for controlling the operation of the SRM according to the current control signal transmitted from the microcomputer 10.
FIG. 2 is a circuit diagram illustrating the inverter circuit unit 20 in detail. As shown in the drawing, the inverter circuit unit 20 includes field effect transistors FET1 to FET5 which are switched by the current control signal transmitted from the microcomputer 10; and current feedback diodes D1 to D6 which control the current applied in motor coils L1 to L3 of each phase of A, B and C.
FIG. 3 is a waveform of the current applied to the motor coils of each phase of A, B and C. When driving the SRM, the optical sensor senses the position and speed of the motor and transmits the sensed signal to the microcomputer 10.
The microcomputer 10 controls the current amount according to the position and speed of the motor and supplies the current to the field effect transistors FET1 and FET2; FET3 and FET4; and FET5 and FET6, successively.
Accordingly, the field effect transistors FET1 to FET6 are switched and then predetermined current waveforms illustrated in FIG. 3 are supplied to the motor coils L1, L2 and L3 of each phase of A, B and C, thereby rotating the SRM.
However, in the conventional SRM, since the current waveforms applied to the motor coils when driving the SRM are constant to the motor speed, noise caused by torque ripple can be generated when rotating the motor at low speed. Moreover, the efficiency of the motor is degraded by a current overlap when rotating the motor at high speed.